1. Field of the Invention
The present invention relates to a tube bank apparatus for distributing stock.
More specifically, the present invention relates to a tube bank apparatus for distributing stock in a headbox of a papermaking machine.
2. Background Information
A conventional headbox distributor uses a tube array to spread the pulp slurry as uniformly as possible across the width of a paper machine headbox prior to the start of the drainage or other thickening process. The tube array is made up of individual round inlet tubes mounted in some manner to cause acceleration of the flow into each tube from a cross machine header or other form of supply of the slurry prior to the tube array. The pressure drop from the acceleration of the flow at the inlet of each tube within the array is critical to the uniformity of the flow within each tube and therefore to the uniformity of the cross machine uniformity of the headbox in general. This acceleration of the flow is also a factor in the operational cleanliness of the headbox operation. The exit end of a typical tube array may take on many shapes but eventually the flows exiting each individual tube must be re-joined prior to or within the nozzle of the headbox prior to discharge to the drainage area. The reorientation of the round tube entrance flow to the eventual rectangular shape of the nozzle will create disturbances in the flow in all directions. These disturbances must be damped or reduced in some way prior to discharge out the slice so as not to cause nonuniformities in the paper web.
The purpose of this invention is to create the necessary pressure drop and subsequent uniform cross machine flow distribution while minimizing the wall effects of the individual tubes prior to the rejoining of the flows in the nozzle. According to the present invention, the discharge end of each tube is of a trapezoidal shape with alternate tube trapezoid shapes vertically opposite each other. These trapezoidal shaped tubes are nested together to form a close packed array on the discharge end, with little or no vertical wall continuous in any area across the width of the headbox. To make the edge effect minimal to the pond sides a special tube can be supplied on each end which has one side the same angle as the two sides of the trapezoidal discharges and the other side vertical. This tube may be larger in the discharge area than the rest of the tubes and subsequently may have a larger inlet as well. This larger inlet may have an adjustable insert for flow and fiber orientation control as well.
The invention uses a distributor consisting of simple round inlet tubes expanding to a round expansion area then to a trapezoidal area with a cross-sectional area similar to a cross-sectional area of the round expansion area. This round to trapezoid allows for some acceleration of the flow toward the discharge of the tube, yet minimizes the vertical open area change between tubes by slanting the wall area between tubes. This invention will reduce cross machine non uniformity of both consistency and velocity of the stock flow. This invention is useful for all grades of paper or tissue, and is usable with or without the inclusion of flow turbulence control sheets. The apparatus according to the present invention is usable with or without the use of consistency dilution control. This invention is adaptable for using different entrance diameters of the tube array which will alter the in-going velocities.
Therefore, the primary feature of the present invention is the provision of a tube bank apparatus for distributing stock in a headbox of a papermaking machine that overcomes the problems associated with the prior art arrangements and which makes a significant contribution to the papermaking art.
Another feature of the present invention is the provision of a tube bank apparatus for distributing stock in a headbox of a papermaking machine that reduces cross machine non uniformity of both consistency and velocity.
Yet another feature of the present invention is the provision of a tube bank apparatus for distributing stock in a headbox of a papermaking machine that increase the operational cleanliness of the headbox operation.
Other features and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description of a preferred embodiment of the present invention contained herein.